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Mr Cable's comments reflect a shift away from the warm relations of the coalition's creation a year ago to a more "businesslike" arrangement expected to prevail following this week's elections and referendum on electoral reform.

The Lib Dems' disastrous showing on Thursday claimed another scalp on Saturday, with the resignation of the party's leader in Scotland, Tavish Scott.

Mr Scott, who was one of only five Lib Dem MSPs to survive the bloodbath at the polls, blamed the Westminster coalition for the party's humiliation at Holyrood.

"I think our ability to demonstrate that we were still Liberal Democrats and not just propping up a Tory Government has not come across in the past year, and that is ultimately why we paid a very, very heavy price on Thursday night," he said.

With Mr Scott's diagnosis widely shared among Lib Dem MPs, the junior coalition partners are expected to seek to assert a distinct identity by putting their foot down over Conservative policies which go beyond the agreement which sealed the coalition last year.

Several senior figures have indicated they will demand changes to Health Secretary Andrew Lansley's plans to hand NHS commissioning to GPs and expand private sector involvement in healthcare provision, which did not feature in the agreement.

Mr Cable said: "We have a coalition agreement which is a very good agreement and which is balanced and which we have to deliver and that is the text around which we should operate in future, while not losing sight of the central purpose of the coalition, which is to sort out this economic mess.

"The health service reforms went some way beyond what was in the coalition agreement and that is going to be a major issue as we go forward."

Mr Cable added: "Some of us never had many illusions about the Conservatives, but they have emerged as ruthless, calculating and thoroughly tribal. But that doesn't mean to say we can't work with them."